LG Power (L22c) SMS Sent but not delivered

Hi folks. I have an LG Power L22c Straight Talk phone that I really enjoy. However occasionally when I send an SMS message I will be told by Textra the message was 'Sent' but never reaches 'Delivered' stage. Sometimes it will take 10-15 minutes for a message to be delivered, or will take that long to receive a message. And then other times, everything will behave just fine.

This has happened in areas with excellent coverage, so it is not a network issue. I have tried multiple SMS apps (Textra, Messaging, Messenger, GoSMS Pro, Hangouts, Chomp) and they all have dealt with the same issue.